1. Field of the Invention
The present invention relates to a semiconductor device and in detail, it relates to a semiconductor device in which a ROM (EEPROM), having a capability to electrically write and erase information in the prescribed storage means, and a ROM (OTPROM), having a capability to electrically write information in the prescribed storage means only one time and no capability to erase, are mixed.
2. Description of the Related Art
Hitherto, semiconductor devices containing a ROM (EEPROM), having capability to electrically write and erase information in the prescribed storage means, and semiconductor devices containing a ROM (OTPROM), having capability to electrically write information in the prescribed storage means only one time and no capability to erase, have been used individually and generally.
However, with the increasing complexity of information processing systems in recent years, plural semiconductor elements having different functions respectively are mounted on the same chip. This allows downsizing the chip, increasing the number of functions, reducing the manufacturing cost and the like.
For example, in many cases, an EEPROM for storing the prescribed program for a microcomputer is contained in one chip, while a OTPROM in which data such as the ID of the used device, that is, information about the manufacturer's serial number, manufacture date and the like, is contained in another chip.
However, since the voltages used for writing and reading information, etc. are different in an EEPROM and in an OTPROM, only an EEPROM or an OTPROM is mounted on a chip (system-on-chip) in many cases, therefore, conventional devices have a defect in that the manufacturing process is made complicated and manufacturing cost is increased.
Although the defect can be dealt with by using a multi-power-supply system in which the EEPROM and the OTPROM are simultaneously mounted on the same chip but the power supplies are individually constituted, this method also has a defect in that the manufacturing process is complicated and the manufacturing cost is increased.
In an ordinary method, the many of the data processing operation can be carried out only with EEPROMs.
However, recently, since it has been required that a lots of amount of information should be processed and registered in memories in a short period, many cases have necessarily been occurred in which the processed information should be stored in OTPROM.
For example, a serial number of a chip can be registered in the read-only-memory having a capability to electrically write and erase information in a storage means (EEPROM) but it can be rewritten by an user of the chip.
Accordingly, in such a situation, even when the user of the chip wishes to check the history of the chip utilizing the serial number, when the chip is malfunctioned, a high reliability about the serial number of the chip stored in the EEPROM, cannot be obtained.
On the other hand, the reliability about data written into the stored in the OTPROM is much higher than that stored in the EEPROM, since the data once stored in the OTPROM is not theoretically erased and thus the data representing the operational conditions of the chip can be sequentially stored in the OTPROM.
Therefore, when the reasons about the malfunction of the chip is analysed, the operational histories of the chip having a high reliability, can be easily obtained.
Thus, it has been required to use a chip on which the EEPROM and the OTPROM are simultaneously provided on the same chip.
However, it has been considered to be difficult that the EEPROM and the OTPROM are simultaneously existed on the same chip. Accordingly, the present invention is to provide a means for resolving the above-mentioned problem.